Dental impression materials



United States Patent 3,268,348 DENTAL IMPRESSION MATERIALS Jacque C.Morrell, 8 Oxford St., Chevy Qhase, Md. No Drawing. Filed Sept. 23,1965, Ser. No. 489,758

23 Claims. (Cl. 106-385) This invention relates to dental impressioncompositions particularly of the alginate type and is acontinuation-1npart of my applications, Serial No. 158,943, filedDecember 8, 1961; now abandoned; and more particularly Serial No.375,957, filed June 17, 1964, which is a continuationin-part of theformer, now US. Patent No. 3,234,033.

A primary objective is to produce compositions WhlCh provide dentalimpressions possessing the qualities of elasticity and resilience aswell as rigidity and toughness or strength so balanced that precisiondental impressions may be made and removed from undercuts withoutrupture or permanent deformation. A specific requirement in dentistry ismaking dentures, both full and partial, as well as bridges, in accuratedental reproduction with maximum comfort to the patient, and this isalso a general objective of my invention.

It is among the further objectives of this invention to produce modelsor casts from such impressions that possess hard smooth surfaces freefrom chalkiness and dusting in handling during use of the same or instorage.

Another important objective of my invention is the production of adental impression composition which is readily wetted and mixed withwater to a smooth consistency with controlled setting time.

A further objective of the invention is to produce dental impressioncompositions which have long storage and shelf life, that is they showminimum or no deterioration with age during use and normal exposure toatmospheric conditions including warm and humid conditions.

Moreover the impressions made from my compositions require no fixing orafter treatment in special solutions or baths which involve additionaltime and material and increased cost generally. The fixing operationrefers to treatment of the impression after it has been made. In theearlier developments and until comparatively recently, this operationwas necessary before pouring or applying the dental stone (generally acomposition containing some form of plaster of Paris) to the impressionto make a satisfactory model or cast. The fixing baths consisted ofaqueous solutions of various inorganic salts and these materials, aswell as the time and cost, are eliminated by the use of my composition.

Among the essential ingredients or components of my invention in itsmajor or primary aspect are (a) the alginates especially the watersoluble types such as the alkali metal alginate, e.g., soditun orpotassium or ammonium alginates, (b) calcium sulphate preferably in thedihydrate form, although the anhydrous and hemi-hydrate types also givegood results; and (c) I also as a principle feature of my invention makeuse of certain selected fluorides specifically barium fluoride, which Ibelieve I am the first to use in detal impression mixtures of the typenoted above. I also make use of the oxides of magnesium and aluminum inthe mixture particularly the former. These oxides generally have theproperty of neutralizing acids. These and other novel combinationshereinafter referred to are employed by me. The amounts of bariumfluoride used in my impression mixture may vary from about 1% to about10% by weight, and preferably from about 1% to about The calciumsulphate in the mixture reacts with the water soluble alginates to forman elastic and resilient impression base on the one hand, and it alsoreacts With the fluorides to form the insoluble calcium fluoride. Thespecific reactions and interreactions of these essential maice terialsand those disclosed herein generally appear to be a prime requirement toproduce the superior results I obtain, and to meet the foregoingobjectives. In addition to these essential ingredients, I also make useof retarders, generally salts of an alkaline character such astetra-sodium pyrophosphate to control the rate of the reactions and toprevent premature setting; and I also make use of fillers such asdiatomaceous earth (and other generally inert and water insolublematerials), for bulk and as a diluent of the more active ingredients.All of the materials are thoroughly mixed and in a finely divided stateof subdivision, and when it is desired to use the resulting composition,it is admixed with water in proper proportions to form the impression,the details of which are fully described hereinafter. These and otheraspects of my invention will be discussed and set forth more fullybelow.

The soluble salts of alginic acid (which is the essential gel formingmaterial in various marine algae or plants), especially the potassium,sodium and ammonium alginates or mixtures of the same are suitable formy invention. The commercial product known as Improved Kelmar has beenfound very satisfactory. Calcium sulphate in the form of the anhydroussalt (CaSO or the hemihydrate (CaSO /2H O) and preferably the dihydrate(CaSO .2H O) may be employed. The soft soluble alginate is convertedinto the resilient and elastic insoluble type in an aqueous medium byinteraction with calcium sulphate. The retarder which controls the rateof setting of the impressionmixture may comprise a salt having analkaline reaction generally such as sodium carbonate or trisodiumorthophosphate or meta phosphate but I prefer the tetrasodiumpyrophosphate for this purpose. With regard to the fillers, I preferdiatomaceous earth (e.g., the commercial product referred to asHyflo-Super-Cal). However, (although less desirable) other substantiallyinert and water insoluble materials such as calcium fluoride, carbonateor triphosphate, as well as various finely divided earths or clays andminerals, e.g., bentonite, talc, kaolin, etc., and various silicatessuch as those of the alkaline earth metals and those of aluminum and theheavier metals, e.g., lead silicate, and as stated previously Waterinsoluble oxides such as, for example, aluminum oxide or magnesium oxidealone or in admixture with the diatomaceous earth, or with each other,could be employed with varying results, especially in addition todiatomaceous earth.

In its principal aspects and as a major feature of my novel impressionmixtures, I make use of barium fluoride in combination with the use ofthe aforementioned alginates and with calcium sulphate as essentialingredients of my composition. The principal reaction of calciumsulphate with the soluble alginate has already been referred to. Thereactions which may occur between the calcium sulphate and bariumfluoride may be explained as follows:

Calcium sulphate is soluble in water to the extent of 0.2% and thefluoride of barium for example, is dissolved to the extent of 0.16%However calcium fluoride is soluble in water only to the extent of0.002%, and the free calcium and fluoride ions furnished by the calciumsulphate and barium fluoride respectively are considerably in excess ofthe concentration required to precipitate them as calcium fluoride. Thereaction thus goes forward until one of the other of the reactants isexhausted. It is thus noted that even with such a small concentration offluoride ions as those furnished by the relatively insoluble bariumfluoride will cause precipitation of the even less soluble calciumfluoride.

Whatever may be the explanation of the reaction in an aqueous medium orsequence of reactions in the mixture in relation to the physicalproperties of the impression and the stone model or cast made from thesame, the result is an impression which is smooth and accurately definedand may be readily removed without breakage or distortion. Moreover, themodel or cast made from these impressions are of a high degree ofprecision and part cleanly from the latter without adhesion and haveglossy, flintlike non-dusting and non-chalking surfaces surfaces of ahighly superior type.

I believe in this connection that I am the first to use barium fluorideand the combinations mentioned herein, in impression mixtures containingthem and in addition containing the other essential ingredients namelythe soluble alignates and calcium sulphate.

The amounts of barium fluoride which I may incorporate in my impressionmixtures may vary from about 1% to about 10% by weight with a preferredrange of from about 2% to about 5% more or less.

It may be noted particularly that the results observed with my newdental compositions employing barium fluoride and various combinationsof the same are greatly superior to the use of mixtures containing thefluorides of the prior art namely those of sodium and potassium or zincwhen used singly.

I am aware that potassium and sodium fluorides have been disclosed inthe prior art and despite the fact that they are both alkali fluoridesthe former is soluble in water to the extent of 92.5% while sodiumfluoride dissolves much less to the extent of 4.5%. Potassium fluorideis very diflicult to handle because it is highly deliquescent, andmoreover the results of making impression mixtures and impressions aresomewhat unreliable because of unpredictable working ranges in time ofmixing, eifect of temperatures, setting times and other controldifiiculties. Mixtures employing sodium fluoride alone are somewhatbetter in these respects than potassium but the results with regard toimpressions and casts in both cases leave much to be desired; and infact when used alone, i.e., as the sole fluoride additive both potassiumand sodium fluoride dental impression compo sitions have been found tobe impractical in actual commercial use.- Moreover I have found that theaddition of barium fluoride to dental impression mixtures containingeither of these two fluorides imp-roves the overall results obtainedwith them. The latter feature comprises another aspect of my inventionnamely adding barium fluoride to dental impression mixtures containingsodium or potassium fluorides.

It is noted also in connection with the prior art that dental impressioncompositions containing zinc fluoride as the sole fluoride give muchbetter results than either potassium or sodium fluoride compositions sofar as control and quality of impression and the cast are concerned butsuch compositions have been found to be notoriously unstable or have ashort shelf life especially in warm and humid environments rendering theproduct useless. In general basic oxides of low water soiubility areused.

In still another aspect of my invention I may add basic metal oxides tothe mixture containing barium fluoride or other basic oxides such asthose of magnesium and aluminum which function as neutralizing agents.

The selected neutralizing agent (which functions under adverseconditions to stabilize the mixture) may be a metal oxide, or hydratedoxide, or carbonate, e. g., of oxides of magnesium, aluminum and thelike. These neutralizing agents are insoluble in water or only slightlysoluble and neutralize acids. Some further examples of these are calciumoxide or carbonate in small amounts and the hydroxides of magnesium oraluminum.

The amounts of these substances used for illustration may be from about1% to about by weight or preferably about 1% to about 5%. It is to benoted in the above connection and in general with this aspect of myinvention that I refer to these oxides as metal oxide neutralizersbecause in general they (as well as the other compounds referred tobelow) show reaction in neutralizing acids, e.g., HF.

Of all of these the oxides are preferred, especially magnesium oxide.Also in those cases where the addition of an oxide or similar acidneutralizing agent is indicated the fluorides corresponding to the oxideadded are very sparingly soluble in water. Moreover in general I may addmetal oxides, or the other types of compounds mentioned on a selectivebasis with regard to the type and various proportions of the componentsof the mixtures employed by me.

Various combinations may be made, as another feature of my inventionwith barium acid fluoride and the oxides of lithium, magnesium,aluminum, zinc and others, or by other suitable methods to produce thecorresponding double fluorides and/or intimate mixtures of the same.Examples of these are BaF .MgF BazF AlF BaF .2LiF; and BaF .ZniF etc.

The reactions may be illustrated by the following:

The results obtained are satisfactory in either case whether thefluorides combine as a loose chemical combination or are used inintimate admixture with each other.

The amounts of each of the combinations shown above used in theimpression mixture referred to above may vary from about 1% to 10% withthe preferred range of 2% to 5%.

The fluoride of barium as pointed out is very much less soluble in waterthan that of potassium (92.5%) and comparatively is much less solublethan sodium fluoride being respectively 4.44% for the latter and 0.16%for barium fluoride. The difierences in chemical and physical propertiesno doubt account for its superiority in the present connection. Thereactions with the mixtures containing alginates and calcium sulphatewith particular reference to the latter are as follows:

The amount of barium fluoride in the type of impression mixtures usedherein are in proportions of from about 1% to about 10% (with 2% to 5%preferred). I may also use the complex addition compounds or mixtures ofthe type previously referred to in the same range.

lt is especially to be employed as stated above in connection with mypresent invention that I may employ barium fluoride (solubility in'Water 0.16%) as the fluoride component of my dental impression mixture,contaming the other components as outlined above in the mixture; andmoreover it'is inherent in this aspect of my invention that bariumfluoride and calcium sulphate must both be specifically present in themixture to obtain the desired results. The reaction with calcium analkaline sulphate (hydrated) is shown below:

It is noted particularly in this reaction that the novel feature ispresented of the formation of two practically insoluble substancesnamely calcium fluoride already referred to, and barium sulphate whichhas the extremely low solubility in water of 0.00035%.

Strontium fluoride (solubility in water 0.12%) reacts similarly tobarium fluoride (although the latter is definitely preferred) to formstrontium sulphate on reaction with calcium sulphate, the solubility ofstrontium sulphate being about the same order as strontium fluoride; andI may if desired use the latter in the dental impression mixture shown.However it is noted that for several reasons I prefer the use of bariumfluoride as an additive. Complex fluorides may ailso be formed with acidfluorides and oxides in these cases. In all cases it is desirable to useneutralizing agent of the types described above including basic metaloxides, hydroxides and the like pref erably magnesium oxide.

Specific examples The table shows a number of specific examples inconnection with various compositions and ingredients each in generalbeing to some degree dependent on the specific type of fluorideemployed, although they need not necessarily be widely different forbest results and, on the other hand, may vary considerably, inaccordance with desired results.

BflFz BaFz BaFzZllFz BZLF ZLiF BaF .l\igFz 2KF.BLF2 Ingredients, Percentby Weight Barium Barium Barium Barium Barium Potassium Fluoride FluorideZine Lithium Magnesium Barium Fluoride Fluoride Fluoride FluoridePotassium Alginate 13. 5 13. 7 13. 8 13. 5 13. 5 13. 5 Calcium SulphateDihydrate 12.8 12. 6 13. 5 12.7 12. 3 12. 5 Retarder TetrasodiumPyrophosphate 2.0 2. O 2. 3 2. 3 1. 5 2. 2 Fluoride, etc. (see above 4.2 4. 2 4. 2 4. 5 4.0 4.3 Magnesium Oxide 0.0 3. 5 4. 5 5. 5 0.0 4. 5Filler Diatomaceous Earth 67.5 64. 61. 7 62.0 68. 8 63. 0 Ex mpl (l) (2)(3) Remarks: Good but non-equivalent results may be obtained alsowith(a) Compositions like Example 6 in which 2N1F.B9.F2 is the fluorideused; (b) Compositions like Example 5 in which B8.F2.A1F3 is thefluoride used; (c) Substitutions oi filler and type of calcium sulphatemay be made with some adjustment of other materials; (d) Variations inthe amount of MgO used.

tures may be used and to the most suitable proportions for their use:The ingredients or components of the compositions of my impressionmixtures which I have referred to above as preferred materials, i.e.,the soluble alginate, e.g., potassium alginate (a suitable form isImproved Kelmar), calcium sulphate dihydrate; the retarder, tetrasodiumpyrophosphate; and barium fluoride.

All of the materials should be in finely divided form, and thoroughlymixed. On a generalized basis, the proportions of materials may varyconsiderably. Satisfactory results may be obtained within the followingillustration of range and intermediate compositions shown forconvenience in parts per one hundred parts by weight or percent;although I am not limited thereto.

Variations in the proportions of ingredients may be on an even widerbasis than shown in the above illustration for example as alreadypointed out, barium may vary from about 1% to 10% and the calciumsulphate, dependent on the type and the extent of hydration and otheringredients from about 10% to about The filler will vary in amount withthe variation in the other ingredients; and where the diatomaceous earthis supplemented by some other filler, e.g., bentonite, kaolin, calciumor magnesium carbonate, etc., the proportions used of the former areless. All of these data are by way of examples and are not to beconstrued as limiting.

In the production of the dental impression material all components oringredients are reduced to finely divided or powdered form and sieved toabout 80 mesh in size, or finer. After mixing in a suitable type ofmechanical mixer (such as a rotary helicoid ribbon type or double coneor other eflicien-t tumbling type) the lumps may be broken down bypassing through a coarse mechanical sieve. At this state, the materialis ready for packaging and distribution for use. Flavoring or coloringmaterials may be introduced after mixing with a small amount ofdiatomaceous earth, calcium or magnesium carbonate or magnesium oxide.

When used by the dentist, the impression material prepared as describedis mixed with water generally at room temperature to the consistency ofa somewhat heavy, smooth, creamy paste-like material. Spatulation of thewet mixture may take place in about one half to one minute, and it isthen transferred to the tray to be applied to the moutli. Generally, thelatter operation takes place in about a minute or a minute and a half,and the material is allowed to set for about three and one-half to 'fourminutes in the mouth; the whole operation consuming about six minutes.The proportion of water used is about 10 to 10.5 gms. of the powderedimpression mixture to about 25 cc. of water, or generally a ration ofabout 2.5 parts of water to 1 part of the material. All of these dataare illustrations only.

All of the above data on use may vary somewhat, those shown beingillustrative of satisfactory conditions for good results.

The temperature of the water, as well as the room temperature, thoughnot critical, have very appreciable effect in the setting time,decreasing with increase in temperature and vice versa. This is inaccord with effect of temperature generally on reaction rates. Generallyroom temperatures, depending on individual taste, varies between about 68 F. and 74 F. and this is satisfactory working range, although goodresults may be obtained in a somewhat wider range with minoradjustments.

Any suitable dental stone (generally a plaster of Paris composition) ofwhich there are a number available, made up to proper consistency withwater, may be employed in making the stone cast or model. Moreover, aspreviously stated, fixing is eliminated, that is the impressions madewith my compositions do not have to be treated in a fixing bath orsolution prior to making the cast or model, and the latter, with the useof my invention, are hard, smooth and durable.

There may be many modifications of my invention without departing fromthe spirit and scope thereof, and any limitations to be imposed shouldbe only those in accordance with the appended claims.

I claim:

1. A dental impression composition consisting essentially of a mixtureof an alkali metal alginate, calcium sulphate, a metal fluoride and aninert filler, the said fluoride consisting of barium fluoride, and beingpresent in an amount of from about 1% to about 10%, said fluoride beingadapted to eliminate fixing of said composition while maintainingcontrolled setting time and minimizing deterioration with age, and toprovide smooth and accurate impressions and casts.

2. A dental impression composition consisting essentially of a mixtureof an alkali metal alginate, hydrated calcium sulphate, a metalfluoride, an inert filler, and a retarder, the said fluoride consistingof barium fluoride and being present in an amount of from about 1% toabout said fluoride being adapted to eliminate fixing of saidcomposition While maintaining controlled setting time and minimizingdeterioration with age, and to provide smooth and accurate impressionsand casts.

3. A dental impression composition consisting essen tially of a mixtureof an alkali metal alginate, calcium sulphate dihydrate, a metalfluoride and an inert filler comprising diatomaceous earth, a retarderconsisting of sodium pyrophosphate, the said fluoride consisting ofbarium fluoride and being present in an amount of from about 1% to about10%, said fluoride being adapted to eliminate fixing of said compositionWhile maintaining controlled setting time and minimizing deteriorationwith age, and to provde smooth and accurate impressions and casts.

4. A dental impression composition consisting essentially of a mixtureof an alkali metal alginate, hydrated calcium sulphate, a metalfluoride, a retarder, magnesium oxide, and an inert filler comprisingdiatomaceous earth, the said fluoride consisting of barium fluoride andbeing present in an amount of from about 1% to about 10%, said fluoridebeing adapted to eliminate fixing of said composition while maintainingcontrolled setting time and minimizing deterioration with age, and toprovide smooth and accurate impressions and casts.

5. A dental impression composition consisting essentially of an aqueoussolution of an alkali metal alginate, hydrated calcium sulphate, a metalfluoride and an inert filler, the said fluoride consisting of bariumfluoride, and being present in an amount of from about 1% to about 10%,said fluoride being adapted to eliminate fixing of said compositionWhile maintaining controlled setting time and minimizing deteriorationwith age, and to provide smooth and accurate impressions and casts.

6. A dental impression composition consisting essentially of a mixtureof an alkali metal alginate, calcium sulphate dihydrate, a metalfluoride and an inert filler comprising diatomaceous earth, a retarderconsisting of sodium pyrophosphate, a neutralizer consisting ofmagnesium oxide, the said fluoride consisting of barium fluoride andbeing present in an amount of from about 1% to about 10%, said fluoridebeing adapted to eliminate fixing of said composition while maintainingcontrolled setting time and minimizing deterioration with age, and toprovide smooth and accurate impressions and casts.

7. A dental impression composition consisting essentially of a mixtureof an alkali alginate, hydrated calcium sulphate, a metal fluoride andan inert filler, the

said fluoride consisting of barium fluoride, and being present in anamount of from about 2% to about 5%, said fluoride being adapted toeliminate fixing of said composition While maintaining controlledsetting time and minimizing deterioration with age, and to providesmooth and accurate impressions and casts.

8. A dental impression composition consisting essentially of a mixtureof an alkali metal alginate, hydrated calcium sulphate, a metalfluoride, an inert filler, and a retarder, the said fluoride consistingof barium fluoride, and being present in an amount of from about 2% toabout 5%, said fluoride being adapted to eliminate fixing of saidcomposition while maintaining controlled setting time 'and minimizingdeterioration with age, and to provide smooth and accurate impressionsand casts.

9. A dental impression composition consisting essentially of a mixtureof an alkali metal alginate, calcium sulphate dihydrate, a metalfluoride, an inert filler comprising cliatomaoeous earth, a retarderconsisting of sodium pyrophosphate, and a neutralizer consisting ofmagnesium oxide, the said fluoride consisting of barium fluoride andbeing present in an amount of from about 2% to about 5%, said fluoridebeing adapted to eliminate fixing of said composition While maintainingcont-rolled setting time and minimizing deterioration with age, and toprovide smooth and accurate impressions and casts.

10. A dental impression composition consisting essentially of a mixtureof an alkali metal alginate, Calcium sulphate, a metal fluoride, a metaloxide neutralizer and an inert filler, the said fluoride consisting ofbarium fluoride, and being present in an amount of from about 1% toabout 10%, said fluoride being adapted to eliminate fixing of saidcomposition while maintaining controlled setting time and minimizingdeterioration with age, and to provide smooth and accurate impressionsand casts.

11. A dental impression composition consisting essentially of a mixtureof an alkali metal alginate, hydrated calcium sulphate, a metalfluoride, a metal oxide neutralizer, an inert filler, and a retarder,the said fluoride consisting of barium fluoride and being present in anamount of from about 1% to about 10%, said fluoride being adapted toeliminate fixing of said composition while maintaining controlledsetting time and minimizing deterioration with age, and to providesmooth and accurate impressions and casts.

12. A dental impression composition consisting essentially of a mixtureof an alkali metal alginate, hydrated calcium sulphate, a metal fluorideand an inert filler, the said fluoride consisting of barium fluoridecombined with another fluoride selected from the group consisting ofpotassium fluoride, sodium fluoride, lithium fluoride, magnesiumfluoride, aluminum fluoride and zinc fluoride and being present in atotal amount of from about 1% to 10% said fluoride being adapted toeliminating fixing of said composition While maintaining controlledsetting time and minimizing deterioration with age, and to providesmooth and accurate impressions and casts.

13. A dental impression composition consisting essentially of a mixtureof an alkali metal alginate, hydrated calcium sulphate, a metal fluorideand an inert filler, the said fluoride consisting of barium fluoridecombined with another fluoride consisting of zinc fluoride and beingpresent in a total amount of from about 1% to 10% said fluoride beingadapted to eliminate fixing of said composition While maintainingcontrolled setting time and minimizing deterioration With age, and toprovide smooth and accurate impressions and casts.

14. A dental impression composition consisting essentially of a mixtureof an alkali metal alginate, hydrated calcium sulphate, a metal fluorideand an inert filler, a retarder, the said fluoride consisting of bariumfluoride combined with another fluoride selected from the groupconsisting of potassium fluoride, sodium fluoride, lithium fluoride,magnesium fluoride, aluminum fluoride and zinc fluoride and beingpresent in a total amount of from about 1% to 10% said fluoride beingadapted to eliminating fixing of said composition while maintainingcontrolled setting time and minimizing deterioration with age, and toprovide smooth and accurate impressions and casts.

15. A dental impression composition consisting essentially of a mixtureof an alkali metal alginate, hydrated calcium sulphate, a metalfluoride, a relatively Water insoluble acidneutralizer, an inert filler,and a retarder, the said fluoride consisting of barium fluoride combinedWith another fluoride consisting of zinc fluoride and being present in atotal amount of from about 1% to 10% said fluoride being adapted toeliminating fixing of said composition while maintaining controlledsetting time and minimizing deterioration with age, and to providesmooth and accurate impressions and casts.

16. A dental impression composition consisting essentially of a mixtureof an alkali metal alginate, calcium sulphate dihydrate, a metalfluoride and an inert tiller consisting of diatomaceous earth, the saidfluoride consisting of barium fluoride combined with another fluorideselected from the group consisting of potassium fluoride, sodiumfluoride, lithium fluoride, magnesium fluoride, aluminum fluoride andzinc fluoride and being present in a total amount of from about 1% toabout 10% said fluoride being adapted to eliminating fixing of saidcomposition While maintaining controlled setting time and minimizingdeterioration with age, and to provide smooth and accurate impressionsand casts.

17. A dental impression composition consisting essentially of a mixtureof an alkali metal alginate, hydrated calcium sulphate, a metal fluorideand an inert filler and a metal oxide neutralizer, the said fluorideconsisting of barium fluoride combined with another fluoride selectedfrom the group consisting of potassium fluoride, sodium fluoride,lithium fluoride, magnesium fluoride, aluminum fluoride and zinefluoride and being present in a total amount of from about 1% to about10% said fluoride being adapted to eliminating fixing of saidcomposition while maintaining controlled setting time and minimizingdeterioration with age, and to provide smooth and accurate impressionsand casts.

18. A dental impression composition consisting essentially of a mixtureof an alkali metal alginate, hydrated calcium sulphate, a metalfluoride, a neutralizer consisting of magnesium oxide, an inert fillerconsisting of diatomaceous earth, and a retarder consisting of sodiumpyrophosphate, the said fluoride consisting of barium fluoride combinedwith another fluoride consisting of zinc fluoride and being present in atotal amount of from about 1% to about 10% said fluoride being adaptedto eliminating fixing of said composition while maintaining controlledsetting time and minimizing deterioration with age, and to providesmooth and accurate impressions and casts.

19. A dental impression composition consisting essentially of a mixtureof an alkali metal alginate, hydrated calcium sulphate, a metal fluorideand an inert filler, a retarder and a metal oxide neutralizer consistingof magnesium oxide, the said fluoride consisting of barium combined withanother fluoride consisting of zinc fluoride and being present in atotal amount of from about 1% to about 10% said fluoride being adaptedto eliminating fixing of said composition While maintaining controlledsetting time and minimizing deterioration with age and to provide smoothand accurate impressions and casts.

20. A dental impression composition consisting essentially of a mixtureof an alkali metal alginate, hydrated calcium sulphate, a metalfluoride, a metal oxide neutralizer consisting of magnesium oxide, aninert filler and a retarder, the said fluoride consisting of bariumfluoride and being present in an amount of from about 1% to about 10%,said fluoride being adapted to eliminate fixing of said compositionwhile maintaining controlled setting time and minimizing deteriorationwith age, and to provide smooth and accurate impressions and casts.

21. A dental impression composition consisting essentially of a mixtureof an alkali metal alginate, calcium sulphate dihydrate, a metalfluoride, a metal oxide neutralizer consisting of magnesium oxide, aninert filler, consisting of diatomaceous earth, and a retarder in thesaid fluoride consisting of barium fluoride and being present in anamount of from about 1% to about 10%, said fluoride being adapted toeliminate fixing of said composition While maintaining controlledsetting time and minimizing deterioration with age, and to providesmooth and accurate impressions and casts.

22. A dental impression composition consisting essentially of an alkalimetal alginate, calcium sulphate, a metal fluoride and an inert filler,the said fluoride being selected from the group consisting of barium andstrontium fluorides and being present in an amount of from about 1% toabout 10%, said fluoride being adapted to eliminate fixing of saidcomposition while maintaining controlled setting time and minimizingdeterioration with age, and to provide smooth and accurate impressionsand casts.

23. A composition for taking dental impressions of the type described inclaim 1 wherein the said composition is dispersed in an aqueous medium.

References Cited by the Examiner UNITED STATES PATENTS 2,623,808 12/1952 Meyer.

2,652,312 9/1953 Fink.

2,769,717 11/1956 Cresson 106-3835 2,824,811 2/ 1958 Erickson et a1.

ALEXANDER H. BRODMERKEL, Primary Examiner. L. HAYES, Assistant Examiner.

6. A DENTAL IMPRESSION COMPOSITION CONSISTING ESSENTIALLY OF A MIXTUREOF AN ALKALI METAL ALGINATE, CALCIUM SULPHATE DIHYDRATE, A METALFLUORIDE AND AN INERT FILLER COMPRISING DIATOMACEOUS EARTH, A RETARDERCONSISTING OF SODIUM PYROPHOSPHATE, A NEUTRALIZER CONSISTING OFMAGNESIUM OXIDE, THE SAID FLUORIDE CONSISTING OF BARIUM FLUORIDE ANDBEING PRESENT IN AN AMOUNT OF FROM ABOUT 1% TO ABOUT 10%, SAID FLUORIDEBEING ADAPTED TO ELIMINATE FIXING OF SAID COMPOSITION WHILE MAINTAININGCONTROLLED SETTING TIME AND MINIMIZING DETERIORATION WITH AGE, AND TOPROVIDE SMOOTH AND ACCURATE IMPRESSIONS AND CASTS.
 17. A DENTALIMPRESSION COMPOSITION CONSISTING ESSENTIALLY OF A MIXTURE OF AN ALKALIMETAL ALGINATE, HYDRATED CALCIUM SULPHATE, A METAL FLUORIDE AND AN INERTFILLER AND A METAL OXIDE NEUTRALIZER, THE SAID FLUORIDE CONSISTING OFBARIUM FLUORIDE COMBINED WITH ANOTHER FLUORIDE SELECTED FROM THE GROUPCONSISING OF POTASSIUM FLUORIDE, SODIUM FLUORIDE, LITHIUM FLUORIDE,MAGNESIUM FLUORIDE, ALUMINUM FLUORIDE AND ZINE FLUORIDE AND BEINGPRESENT IN A TOTAL AMOUNT OF FROM ABOUT 1% TO ABOUT 10% SAID FLUORIDEBEING ADAPTED TO ELIMINATING FIXING OF SAID COMPOSITION WHILEMAINTAINING CONTROLLED SETTING TIME AND MINIMIZING DETERIORATION WITHAGE, AND TO PROVIDE SMOOTH AND ACCURATE IMPRESSIONS AND CASTS.